The development of industry and the encroachment of civilization upon established ecosystems often places the interests of commerce at odds with the need to maintain a delicate balance in the ecosystem involved. Consequently, it has become increasingly important to establish the presence, persistence, biological availability, and biological effect of chemical contaminants introduced or about to be introduced into ecosystems using biological monitoring and toxicity testing procedures.
Insects have played a prominent role in toxicity testing and biological field monitoring for environmental contaminants. Standard methods have been established for raising and experimenting with a wide variety of terrestrial species in laboratories, whereas toxicity testing in water, especially freshwater stream and river ecosystems, has relied primarily upon fish and a few noninsect invertebrates, mainly Crustacea (e.g., Daphnia magna, D. pulex, Ceriodaphnia sp., Artemia sp., Hyalella azteca, Grammarus lacustris and the like). Unfortunately, many test species being used are not representative of the most species rich, abundant and productive group of organisms inhabiting streams and rivers, namely, aquatic insects. Aquatic insects are also potentially the group of organisms most vulnerable to the intrusion of toxins into the ecosystem.
Only a few species of aquatic insects such as the nonbiting midges Chironomus tentans and C. riparius and the burrowing mayflies Hexagenia rigida and H. limbata have been used routinely in bioassay studies, both chronic and acute. However, such species are less than ideal. For example, Hexagenia is difficult to culture and usually reproduces only once a year at most, making whole-life bioassays practically impossible. Species such as C. tentans has a shorter developmental period but are nevertheless difficult to work with because of the problems involved in mating adults, initiating experiments with genetically unknown and non-uniform size larvae, handling small eggs, and so on. Both Hexagenia and Chironomus tend to be sediment dwellers, inhabiting large lakes and rivers (Hexagenia) or predominantly lentic (Chironomus) rather than lotic habitats. Thus, they are well suited for sediment bioassays but not for other types of assays.
Although insects are the principal consumer organisms in most stream and river ecosystems worldwide, there is a paucity of stream insect species available as standard test organisms for laboratory and field bioassay procedures. This deficiency arises because it is difficult to establish laboratory colonies when, typically, stream and river insect larvae must be reared in a flowing water system in order to satisfy respiration and/or feeding requirements. Further, stream and river insects generally have long life cycles (e.g., 6-12 months) and the adults often have unusual behavioral requirements for reproduction such as elaborate mating swarms or flights, which make the establishment of laboratory colonies unfeasible.
Accordingly, it is important to provide a new bioassay organism which typifies higher animals in toxicity testing and biological field monitoring while representing the most vulnerable as well as the principal consumer organisms in most stream and river ecosystems. Further, the new bioassay organism must have a short life cycle and strictly controllable reproduction requirements while being amenable to analysis using any suitable procedure. The stream mayfly, (Insecta: Ephemeroptera) Centroptilum triangulifer McDunnough (hereinafter C. triangulifer), satisfies these criteria and overcomes the problems mentioned above relating to the use of other aquatic organisms as bioassay organisms.